The application is based on application No. 98-44308 filed in the Korean Industrial Property Office on Oct. 22, 1998, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The invention relates to supported metallocene catalysts, their preparation, and their use in the polymerization and/or copolymerization of olefins. More particularly, this invention relates to a supported olefin polymerization catalyst prepared by a new process and its use for the polymerization of olefins.
Specifically, in a supported olefin polymerization catalyst prepared by such a process, the catalytically active species is deeply impregnated into the interior pore space of the support and evenly distributed throughout the porous support. Additionally, a novel preparation process does not lead to agglomeration of the catalyst particles. The catalyst of the invention operates in both a slurry polymerization and a gas phase polymerization. The catalyst produces granular olefin polymers with high polymerization activity. Moreover the catalyst can yield high bulk density olefin polymers without reactor fouling and reactor carrier-line plugging and can significantly reduce the production of fines.
(b) Description of the Related Art
Ethylene or xcex1-olefins including ethylene have been polymerized (homo- or copolymerized) by using titanium based catalyst systems composed of titanium compounds and a cocatalyst based on aluminum alkyls, or by using vanadium based catalyst systems composed of vanadium compounds and a cocatalyst based on aluminum alkyls. Recently, homogeneous or supported catalyst systems, based on metallocene compounds and aluminoxane or an ionizing compound as a activator, have also been useful in the polymerization of ethylene and copolymerization of ethylene/xcex1-olefin.
xe2x80x9cMetallocenexe2x80x9d compounds refer to a derivative of a cyclopentadienyl metal complex which is a transition metal compound containing at least one cyclopentadienyl group bonded to a transition metal. The transition metal is selected from Groups 4b and 5b, preferably titanium, zirconium, hafnium. A number of metallocene compounds have been used to produce olefin polymers and copolymers.
Generally, metallocene compounds in combination with an activator have been used to produce olefin polymers or copolymers with high polymerization activity. The terms xe2x80x9ccocatalystsxe2x80x9d and xe2x80x9cactivatorsxe2x80x9d are used interchangeably and are defined to be any compound or component which can activate a metallocene. These activators include aluminoxane (MAO), noncoordinating anions (ionizing compounds such as tri(n-butyl) ammonium tetra bis(pentafluorophenyl)boron or N,N-dimethylanilinium tetra (pentafluorophenyl)borate), which ionize the neutral metallocene compound. It is within the scope of this invention to use aluminoxane as an activator.
The catalyst system formed from the metallocene: and aluminoxane compound is generally referred to as a homogeneous catalyst system since the majority of this catalyst system is soluble in the reaction media and, in most cases, processes for the preparation of ethylene/xcex1-olefin copolymers using this homogeneous catalyst system are applicable only to the solution polymerization system. However, when it is desired to produce high molecular weight polymers by using this catalyst, many inconveniences, such as a markedly increased viscosity of the solution media containing the resulting polymer, reduce polymerization productivity. Additionally, there are problems in that the resulting polymers have low bulk density and it is also difficult to obtain good morphological polymers with excellent particle characteristics. Also this homogeneous metallocene catalyst system has a tendency toward fouling and/or sheeting in a slurry and gas phase polymerization situation, and produces polymer fines which can be detrimental to commercial facilities.
Particularly in a continuous slurry process, fouling on the walls of the reactor which act as a heat transfer surface can result in many problems, including poor heat transfer in the polymerization process. Polymer particles that adhere to the walls of the reactor continue to polymerize and often fuse together and form chunks, which can be detrimental to a continuous process, particularly a fluid-bed process.
In a continuous gas phase process, recycled stream is continuously employed. The recycled stream is heated by the heat of polymerization, and in another part of the cycle (a heat exchanger), heat is removed by a cooling system external to the reactor. Fouling in a continuous gas phase process can lead to the ineffective operation of various reactor systems, for example the cooling system, temperature sensors, gas analyzing sensors, transfer pipes, and the gas distributor, which are often employed in a gas phase fluid-bed polymerization process.
Attempts to overcome the reactor operability issues associated with using metallocene catalyst systems, have resulted in the development of various techniques for supporting or producing a metallocene catalyst system with reduced tendencies for fouling. While all these possible solutions might reduce fouling or sheeting somewhat, some are not economical to employ and/or may not reduce both fouling and sheeting to a level sufficient for the successful operation of a continuous process, particularly a commercial or large-scale process.
Many attempts have been made to polymerize olefins in slurry or gas phase polymerization systems by using a catalyst composed of a metallocene compound and an aluminoxane, and at least one of the compounds has been supported on a porous inorganic oxide carrier, such as silica, alumina, and silica-alumina or mixtures thereof. For example, U.S. Pat. No. 4,937,217 describes a mixture of alkyl aluminums, such as trimethylaluminum and triethylaluminum added to an undehydrated silica to which a metallocene component is then added. U.S. Pat. Nos. 4,912,075, 4,937,301, and 4,935,397 generally describe the adding of trimethylaluminum to an undehydrated silica and then adding a metallocene to form a dry supported catalyst system. U.S. Pat. Nos. 5,008,228, 5,086,025, and 5,147,949 generally describe making a dry supported catalyst system by the addition of trimethylaluminum to a water impregnated silica to form aluminoxane in situ and then adding the metallocene. U.S. Pat. Nos. 4,808,561, 4,897,455, and 4,701,432 describe techniques to form a supported catalyst system where the inert carrier, typically silica, is calcined and contacted with a metallocene and an activator component. U.S. Pat. No. 5,238,892 describes forming a dry supported catalyst system by mixing a metallocene with an alkyl aluminum and then adding undehydrated silica. U.S. Pat. No. 5,240,894 generally describes forming a supported metallocene/aluminoxane catalyst system by forming a metallocene/ aluminoxane reaction solution, adding a porous carrier to the solution, and evaporating the resulting slurry to remove residual solvent from the carrier, and the formed catalyst precursor is possibly subjected to prepolymerization. WO 94121691 describes forming a supported metallocene/aluminoxane catalyst system by forming a metallocene and aluminoxane reaction solution, contacting a porous carrier to the solution, wherein a volume of reaction solution is no greater than the total pore volume of said dehydrated silica, and then drying the catalyst under flowing nitrogen to remove residual solvent from the solid. U.S. Pat. Nos. 5,001,205, 5,308,816, and 5,455,316 describe forming a solid supported catalyst system by adding aluminoxane to a calcined silica and then adding a metallocene, decanting the resulting slurry to remove residual solvent, and washing. Thereafter the formed solid catalyst is possibly coated by a prepolymerization of olefins to improve the poor morphology of the original catalyst.
In prior art, the catalyst component solution does not penetrate into the capillary pores of the carrier, and the active catalyst components is precipitated on the surface of the support particle during the evaporation of solvent, and so the active catalyst components are unevenly distributed on the carrier. Some cases are multi-step and involve a lengthy preparation process, and a relatively low catalyst activity. Particularly when the catalyst is used in polymerization, there is a tendency to cause plugging problems during polymerization. In a slurry polymerization process, when the soluble catalyst portion is leaching out of the porous support and the polymer chains are grown from that, fines within the reactor often accumulated and cling or stick to the walls of a reactor. Polymer fines that adhere to the internal surfaces of reactor can continue to polymerize and result in fouling and plugging of the reactor, which can be detrimental to continuous and batch polymerization processes.
To overcome the unstability of the catalyst components on the support, U.S. Pat. Nos. 5,399,636, 5,466,766, and 5,473,020, as well as U.S. patent application Ser. No. 08/898,460 describe preparing a metallocene catalyst system which is chemically bonded on the organic or inorganic support. However, these methods have the problems involving a multi-step and lengthy preparation process, the removal of impurities, many isolation steps, and high cost or limitation of catalyst activity.
The object of the present invention is to provide a new process for the preparation of a supported olefin polymerization catalyst. The invention is to provide to supply a supported olefin polymerization catalyst, reproducibly prepared by such a process, in which the catalyst components are deeply penetrated into the capillary pores of the support, and the catalyst species are uniformly distributed on the overall support.
The invention also aims at a supported olefin polymerization catalyst capable of producing good morphorogical olefin polymers with relatively high polymerization activity and, moreover, significantly reducing reactor-fouling and fines-production, and the preparation processes of such olefin polymerization catalyst as mentioned above.
Another object of the present invention is to provide a process capable of preparing olefin polymers having high bulk density and spherical olefin polymers with excellent particle characteristics at a high yield when one or more olefin monomers are (co)polymerized without another activator in process, using the supported olefin polymerization catalyst systems as mentioned above.